U.S. Pat. No. 6,022,351 (the disclosure of which is hereby incorporated by reference herein) has provided a significant advance in the art of bone fastening systems during surgical or related medical procedures, in reattaching a skull flap. The invention provides an improvement over the system and method of the U.S. Pat. No. 6,022,351 patent, particularly in providing an enhanced force holding the shank in engagement with the skull and skull flap, and in addition other features are provided that facilitate holding the locking element in place, and facilitate maintaining the fastener and locking elements clamped together in a position holding the skull flap in place. These advantageous results are provided according to the present invention by utilizing a plurality of ridges extending from the fastener head generally perpendicular to the ratchet teeth, and extending upwardly from the fastener shank substantially flat surfaces; by providing a plurality of force concentrating projections on the locking element disc extending axially with respect to the disc; and by providing side walls on the shank having approximately the height of the ratchet teeth, and engaged in side portions of the opening in the locking element.
According to one aspect of the present invention there is provided a fastening system comprising: A fastener element of bio-compatible radiolucent plastic material comprising a substantially disc shaped head and a shank. The shank having substantially flat first and second substantially parallel surfaces, the surfaces having ratchet teeth thereon. A substantially disc shaped lock element of bio-compatible radiolucent rigid plastic material having a through extending opening and locking teeth defining at least part of the opening, the locking teeth cooperating with the ratchet teeth to allow the shank to pass through the opening so that the head and lock element can be forced toward each other, but not allowing movement away from each other. And, a plurality of ridges extending upwardly from at least one of the first and second substantially parallel surfaces adjacent the head, the ridges extending substantially perpendicular to the ratchet teeth.
The ridges may be of two different types, both of which provide a force holding the shank in engagement with the skull and skull flap. The first type of ridges may be of relatively soft plastic, and constructed so that in use the ridges bend or collapse and provide a wedging action against a bone surface engaged thereby. Another alternative is to provide the ridges out of a hard plastic or metal and construct them so that in use the ridges cut locking grooves in a bone surface engaged thereby. In either case the stability of the fastening system is enhanced, as is its ability to hold the skull flap properly in place.
The ridges may be about 3-7 mm long, and typically substantially abut the fastener head. Desirably the ridges upstand from both the first and second surfaces of the shank, and the distance from the tip of a ridge extending upwardly from the first surface to the tip of a ridge extending upwardly from the second surface is between about 2-5 mm, most desirably about 3-3.5 mm. Typically between two and six ridges are provided (extending upwardly from each of the first and second surfaces). The shank may have a thickness of about 1-1.5 mm.
Also the shank may have first and second exterior side walls extending over a portion of the length thereof including past the ridges, and at least some of the ratchet teeth. The locking element opening has first and second side portions for receiving the side walls. For example the side walls extend upwardly past the first and second shank surfaces a distance approximately equal to the heights of the ratchet teeth, and less than the height of the ridges. For example in one embodiment the shank has a basic thickness of about 1 mm, and at the side walls a thickness of about 2 mm, and at the ridges a thickness of about 3 mm.
The lock element typically has first and second faces and a plurality of force concentrating projections extending outwardly from the first face, toward the fastener head in use. The locking teeth also typically extend outwardly from the first face. The fastener head may have a plurality of resilient outrigger leaves, which may be deformed during the clamping operation, to provide a force enhancing the clamping action.
According to another aspect of the present invention there is provided a method of reattaching a skull flap, removed during brain surgery and leaving an opening in a patient""s skull, the flap having an area less than the area of the opening but substantially the same shape, and using a fastening system, comprising a fastener element made of bio-compatible radiolucent rigid plastic having a shank with ratchet teeth and a substantially disc shaped lock element with an opening defined at least in part by at least one locking tooth, and a plurality of ridges upstanding from the shank and extending substantially perpendicular to the ratchet teeth. The method comprises: (a) Placing a plurality of fastener heads, with shanks facing outwardly, in the skull opening. (b) Placing the skull flap in the skull opening so that a gap is provided between the outer periphery of the skill flap and the periphery of the skull opening, and the fastener shanks extend through the gap and the ridges engage at least one of the skull and the skull flap and provide a force holding the shank in operative engagement with the skull and skull flap. (c) Placing the lock elements over the shanks. (d) For each fastener forcing the lock toward the head so that the ratchet teeth and at least one locking tooth move with respect to each other, until the head and lock element are locked together holding the skull flap in a position closing the skull opening. And, (e) removing substantially all shank portions extending outwardly from the lock elements.
In the method (b) may be practiced so that the ridges engage both the skull and the skull flap. When the ridges are of soft plastic and constructed so that they bend or collapse, then (b) is practiced so that the ridges bend or collapse so as to provide a wedging action holding the shank between the skull and skull flap. When the ridges are of hard plastic or metal and are constructed so that they can cut locking grooves into the bone, then (b) is practiced so as to cut locking grooves in the skull and skull flap so as to lock the shank in place therebetween. When a locking element has a plurality of substantially axially extending force concentrating projections, then (d) is practiced so as to cause the force concentrating projection to engage at least one of the skull and skull flap to enhance securement of the locking element to the skull and/or skull flap. Preferably (d) is practiced so that the force concentrating elements operatively engage both the skull and skull flap.
According to another aspect of the present invention there is provided a fastener system comprising: A fastener element of bio-compatible radiolucent rigid plastic material comprising a substantially disc shaped head and a shank. The shank having a plurality of ratchet teeth thereon, and a thickness of about 7 mm or less. A substantially disc shaped lock of bio-compatible radiolucent plastic material having a through extending opening into at least one locking tooth defining at least part of the opening, the at least one locking tooth cooperating with the ratchet teeth to allow the shank to pass through the opening so that the head and lock can be forced toward each other, but not allowing movement away from each other. And, wherein the lock element has first and second faces, and a plurality of force concentrating projections extending outwardly from the first face, toward the head in use. The details of the first concentrating projections may be as set forth above.
According to another aspect of the present invention there is provided a fastener system comprising: A fastener element of bio-compatible radiolucent rigid plastic material comprising a substantially disc shaped head and a shank. The shank having a plurality of ratchet teeth thereon, and a thickness of about 7 mm or less. A substantially disc shaped lock of bio-compatible radiolucent plastic material having a through extending opening into at least one locking tooth defining at least part of the opening, the at least one locking tooth cooperating with the ratchet teeth to allow the shank to pass through the opening so that the head and lock can be forced toward each other, but not allowing movement away from each other. And, wherein the head has a plurality of resilient outrigger leaves.
For example in the fastening system set forth above, the shank has a plurality of ridges substantially abutting the head and extending substantially perpendicular to the ratchet teeth a distance of about 3-7 mm from the head; and typically the shank itself has a thickness of about 1-1.5 mm, and the shank including the ridges has a thickness of about 2-5 mm.
According to yet another aspect of the present invention there is provided a fastener system comprising: A fastener element of bio-compatible radiolucent rigid plastic material comprising a substantially disc shaped head and a shank. The shank having a plurality of ratchet teeth thereon, and a thickness of about 7 mm or less. A substantially disc shaped lock of bio-compatible radiolucent plastic material having a through extending opening into at least one locking tooth defining at least part of the opening, the at least one locking tooth cooperating with the ratchet teeth to allow the shank to pass through the opening so that the head and lock can be forced toward each other, but not allowing movement away from each other. And, wherein the shank has first and second exterior side walls extending over a portion of the length thereof including past at least some of the ratchet teeth; and wherein the locking element opening has first and second side portions for receiving the side walls. In this embodiment typically the side walls extend past the first and second shank surfaces a distance approximately equal to the height of the ratchet teeth, e.g. the total thickness of the shank at the side walls is about 2 mm.
It is the primary object of the present invention to provide an enhanced fastening system, and method of utilization thereof, particularly suitable for reattaching a skull flap in a skull after brain surgery. However the invention has other uses in association with other bones and suitable medical procedures. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.